gnu.crypto.key.srp6
Class SRP6KeyAgreement

java.lang.Object
  gnu.crypto.key.BaseKeyAgreementParty
      gnu.crypto.key.srp6.SRP6KeyAgreement

All Implemented Interfaces:

IKeyAgreementParty

Direct Known Subclasses:

SRP6Host, SRP6TLSClient, SRP6TLSServer, SRP6User

public abstract class SRP6KeyAgreement

extends BaseKeyAgreementParty

The Secure Remote Password (SRP) key agreement protocol, also known as SRP-6, is designed by Thomas J. Wu (see references). The protocol, and its elements are described as follows:

 N    A large safe prime (N = 2q+1, where q is prime)
      All arithmetic is done modulo N.
 g    A generator modulo N
 s    User's salt
 I    Username
 p    Cleartext Password
 H()  One-way hash function
 ^    (Modular) Exponentiation
 u    Random scrambling parameter
 a,b  Secret ephemeral values
 A,B  Public ephemeral values
 x    Private key (derived from p and s)
 v    Password verifier

 The host stores passwords using the following formula:
 x = H(s, p)               (s is chosen randomly)
 v = g^x                   (computes password verifier)

 The host then keeps {I, s, v} in its password database.

 The authentication protocol itself goes as follows:
 User -> Host:  I, A = g^a         (identifies self, a = random number)
 Host -> User:  s, B = 3v + g^b    (sends salt, b = random number)

 Both:  u = H(A, B)

 User:  x = H(s, p)                (user enters password)
 User:  S = (B - 3g^x) ^ (a + ux)  (computes session key)
 User:  K = H(S)

 Host:  S = (Av^u) ^ b             (computes session key)
 Host:  K = H(S)
 

Reference:

1. SRP Protocol Design
   Thomas J. Wu.

Version:

$Revision: 1.2 $

Field Summary

protected java.math.BigInteger	g
static java.lang.String	GENERATOR
static java.lang.String	HASH_FUNCTION
static java.lang.String	HOST_PASSWORD_DB
protected java.math.BigInteger	K The shared secret key.
protected IMessageDigest	mda
protected java.math.BigInteger	N
static java.lang.String	SHARED_MODULUS
static java.lang.String	SOURCE_OF_RANDOMNESS
protected static java.math.BigInteger	THREE
static java.lang.String	USER_IDENTITY
static java.lang.String	USER_PASSWORD

Fields inherited from class gnu.crypto.key.BaseKeyAgreementParty

complete, initialised, name, rnd, step, TWO

Constructor Summary

protected

SRP6KeyAgreement()

Method Summary

protected void	engineReset()
protected byte[]	engineSharedSecret()
protected java.math.BigInteger	uValue(java.math.BigInteger A, java.math.BigInteger B)

Methods inherited from class gnu.crypto.key.BaseKeyAgreementParty

engineInit, engineProcessMessage, getSharedSecret, init, isComplete, name, nextRandomBytes, processMessage, reset

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

SOURCE_OF_RANDOMNESS

public static final java.lang.String SOURCE_OF_RANDOMNESS

See Also:

Constant Field Values

SHARED_MODULUS

public static final java.lang.String SHARED_MODULUS

See Also:

Constant Field Values

GENERATOR

public static final java.lang.String GENERATOR

See Also:

Constant Field Values

HASH_FUNCTION

public static final java.lang.String HASH_FUNCTION

See Also:

Constant Field Values

USER_IDENTITY

public static final java.lang.String USER_IDENTITY

See Also:

Constant Field Values

USER_PASSWORD

public static final java.lang.String USER_PASSWORD

See Also:

Constant Field Values

HOST_PASSWORD_DB

public static final java.lang.String HOST_PASSWORD_DB

See Also:

Constant Field Values

THREE

protected static final java.math.BigInteger THREE

mda

protected IMessageDigest mda

N

protected java.math.BigInteger N

g

protected java.math.BigInteger g

K

protected java.math.BigInteger K

The shared secret key.

Constructor Detail

SRP6KeyAgreement

protected SRP6KeyAgreement()

Method Detail

engineSharedSecret

protected byte[] engineSharedSecret()
                             throws KeyAgreementException

Specified by:

engineSharedSecret in class BaseKeyAgreementParty

Throws:

KeyAgreementException

engineReset

protected void engineReset()

Specified by:

engineReset in class BaseKeyAgreementParty

uValue

protected java.math.BigInteger uValue(java.math.BigInteger A,
                                      java.math.BigInteger B)